Feature Request: Add file extensions to the ACME challenge files

[snayagar-crono]

If you're having trouble using Certbot and aren't sure you've found a bug or
request for a new feature, please first try asking for help at
https://community.letsencrypt.org/. There is a much larger community there of
people familiar with the project who will be able to more quickly answer your
questions.

My operating system is (include version):

I installed Certbot with (snap, OS package manager, pip, certbot-auto, etc):

I ran this command and it produced this output:

Certbot's behavior differed from what I expected because:

Here is a Certbot log showing the issue (if available):

Logs are stored in /var/log/letsencrypt by default. Feel free to redact domains, e-mail and IP addresses as you see fit.

Here is the relevant nginx server block or Apache virtualhost for the domain I am configuring: